Suspects tied to Boston bombings – Dias Kadyrbayev, left, with Boston Marathon bombing suspect Dzhokhar Tsamaev in a picture taken from the social media site VK.com. Kadyrbayev is expected to plead guilty August 21 to charges in connection with removing a backpack and computer from Tsamaev's dorm room after the April 2013 bombing, according to a defense lawyer.

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Suspects tied to Boston bombings – Bombing suspect Tamerlan Tsarnaev was killed during the shootout with police in Watertown, Massachusetts, on April 19, 2013. He is pictured here at the 2010 New England Golden Gloves.

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Suspects tied to Boston bombings – Dzhokhar Tsarnaev was captured in a Boston suburb on April 19, 2013, after a manhunt that shut down the city. In July, he pleaded not guilty to killing four people and wounding more than 200.

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Suspects tied to Boston bombings – From left, Azamat Tazhayakov and Dias Kadyrbayev went with Boston bombing suspect Dzhokhar Tsarnaev to Times Square in this photo taken from the social media site VK.com. A federal grand jury charged Tazhayakov and Kadyrbayev with obstructing justice and conspiracy to obstruct justice relating to the removal of a backpack from Tsarnaev's dorm room after the bombings. Tazhayakov was convicted of conspiracy and obstruction charges in July 2014. He faces up to 25 years in prison at his sentencing in October. He has filed an appeal.

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Suspects tied to Boston bombings – Robel Phillipos, a U.S. citizen, was also arrested on May 1, 2013. He was charged with lying to federal agents about the bombing, according to court papers.

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Suspects tied to Boston bombings – Phillipos, Tazhayakov and Kadyrbayev are accused of removing items from Tsarnaev's dorm room after the bombings on April 15, 2013. The items they took included a backpack containing fireworks that had been "opened and emptied of powder," according to the affidavit.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men identified as Suspect 1 and Suspect 2 in the deadly bombings at the Boston Marathon. They were later identified as Dzhokhar Tsarnaev, 19, and his brother Tamerlan Tsarnaev, 26.

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Suspects tied to Boston bombings – Boston Police released surveillance images of Dzhokhar Tsarnaev at a convenience store on April 19, 2013.

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Suspects tied to Boston bombings – The FBI tweeted this photo on April 19, 2013, and urged Watertown residents to stay indoors as they searched for the second suspect.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men it called suspects in the deadly bombings and pleaded for public help in identifying them. The men were photographed walking together near the finish line.

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Suspects tied to Boston bombings – A man identified as Suspect 2 appeared in this photograph by bystander David Green, who took the photo after completing the Boston Marathon. Green submitted the photo to the FBI, he told Piers Morgan in an interview.

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Suspects tied to Boston bombings – The man identified as Suspect 2 appears in a tighter crop of David Green's photo.

Story highlights

Three friends of Boston bombing suspect Dzhokhar Tsarnaev are charged in federal court

Affidavit shows actions, communications after Boston suspects' photos went out

The friends went to Tsarnaev's dorm, found a backpack with fireworks with the powder out

They took this backpack and threw it away, the affidavit released Wednesday states

When Dzhokhar Tsarnaev got a text from a friend asking him if he was one of the two men shown in FBI-released photos of Boston bombing suspects, his reply was short and light: LOL.

Other messages from the teenager followed, including "You better not text me" and "Come to my room and take whatever you want," according to an FBI affidavit released Wednesday. His friend took the texts as jokes, as if Tsarnaev found humor in the mere idea that he could be responsible for such horror.

But when Dias Kadyrbayev showed one of their mutual friends that last text, the friend wasn't laughing.

"He believed he would never see Tsarnaev alive again," the affidavit said of Azamat Tazhayakov.

What Kadyrbayev, Tazhayakov and another friend, Robel Phillipos, did next is the subject of a detailed, sometimes complex FBI affidavit released on Wednesday. That document lays out the federal case as to why the three young men, like their friend Tsarnaev, are now in federal custody.

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The charges levied Wednesday do not accuse the three friends of having any involvement in the April 15 attack. Lawyers for two of the men insist that their clients are cooperating and deny any such role.

Did they suspect Tsarnaev could be responsible for such bloodshed? According to Tazhayakov's account in the affidavit, while they were eating together about a month before the bombing, Tsarnaev told them he knew how to make a bomb. Less clear, and more critical to their case, was when they concluded Tsarnaev was possibly involved in the Boston attacks, and what they did afterward.

And were their actions -- both in tossing a backpack belonging to Tsarnaev and how they dealt with federal investigators -- criminal? That may be decided by a jury, unless the charges are dropped or plea agreements are reached.

What is known is that the four young men -- Tsarnaev, Phillipos, Kadyrbayev and Tazhayakov -- enrolled in fall 2011 at the University of Massachusetts-Dartmouth and became friends.

Kadyrbayev and Tazhayakov were in the United States on student visas from Kazakhstan, and spoke Russian as did Tsarnaev. Phillipos, a high school classmate of Tsarnaev, called Cambridge, Massachusetts, his home, as did Tsarnaev.

They hung out together, went out together -- including to New York's Times Square, as a 2012 photo with Kadyrbayev, Tazhayakov and Tsarnaev showed. Kadyrbayev told investigators that he'd gotten to know Tsarnaev's family and had repeatedly gone to his home when the family lived in Cambridge.

And they spent time together after the deadly Boston Marathon blasts.

Two days after that attack, on April 17, Kadyrbayev told law enforcement officers that he drove to Tsarnaev's dormitory room on the campus of their southern Massachusetts school and texted to his friend to come down to meet him. Tsarnaev -- who had noticeably shorter hair at the time, Kadyrbayev recalled -- came down, the two chatted, and that was that.

Tsarnaev spent that night, until around midnight, at the New Bedford apartment of Tazhayakov. The next afternoon, Tazhayakov went to class on campus and got a ride home from Tsarnaev, the federal affidavit states.

That happened not long before 5 p.m., when the FBI released its first photos of the two Boston bombing suspects. One wore a dark baseball cap, a light collarless shirt and a dark-colored jacket. The other had a hooded sweatshirt, black jacket and a white baseball cap turned backward.

It was the latter suspect that caught Phillipos' eye. And it also got the attention of Kadyrbayev, when he got home that night and turned on the TV.

Could that be Dzhokhar?

The night of Thursday, April 18, authorities say that Dzhokhar and Tamerlan Tsarnaev were on the run -- allegedly responsible for killing a Massachusetts Institute of Technology police officer, carjacking a Mercedes SUV, then tossing explosives and trading gunfire with authorities on a high-speed chase through Boston suburbs.

Dzhokhar Tsarnaev's friends were active that night as well, some 60 miles south.

While the three 19-year-olds offered slightly different details and time frames, a common chain of events emerges from their remarks to investigators as laid out in the FBI affidavit.

At some point, they exchanged texts about the "news" and agreed to meet at Dzhokhar Tsarnaev's dorm room in Dartmouth.

Tsarnaev's roommate let them in, saying Tsarnaev had left a few hours earlier, according to Kadyrbayev. It was around then that Tazhayakov says that Kadyrbayev showed them a text message from Tsarnaev that they could take whatever they needed from his room -- which Tazhayakov interpreted as meaning he'd never be back.

While watching a movie, one or more of them spotted a backpack. Phillipos -- who at first denied to investigators ever going to the dorm room, then later changed his story, the affidavit states -- said Kadyrbayev found it when he "went through (Tsarnaev's) belongings." Inside, Phillipos noticed about seven tubular fireworks, each between 6 to 8 inches long. The fireworks' powder had been taken out.

That wasn't all they found. Kadyrbayev also came across a jar of Vaseline that he thought Dzhokhar Tsarnaev used "to make bombs," according to the affidavit.

By then, the same document states, Kadyrbayev knew Dzhokhar Tsarnaev was involved in the Marathon bombing -- a judgment that his lawyer, Robert Stahl, disputed Wednesday, saying "his first inkling came much later."

Whatever their rationale -- be it to help a friend or cover up for him -- the three men left with the backpack. Kadyrbayev said he took Tsarnaev's laptop computer too, because he felt Tsarnaev's roommate might get suspicious if they left with the backpack alone, the affidavit states.

They all ended up at Kadyrbayev's and Tazhayakov's New Bedford apartment. There they saw the news coverage on the bombings, wallpapered with photos of the two suspects.

Kadyrbayev and Tazhayakov "started to freak out, because it became clear from a CNN report that we were watching that (Dzhokhar Tsarnaev) was one of the Boston Marathon bombers," Phillipos told investigators.

The Cambridge resident said he didn't understand much of what Kadyrbayev and Tazhayakov said afterward because they talked mostly in Russian.

At some point though -- Kadyrbayev said it was later that night, Tazhayakov thought it was early the following morning -- Tsarnaev's backpack was put in a black garbage bag, lugged outside, and thrown in a dumpster.

This came after all three friends talked about what to do first, according to the affidavit. Phillipos' response, for instance, to Kadyrbayev: "Do what you have to do."

A garbage truck emptied that dumpster that Friday -- the same day that Tsarnaev was finally captured, hurting from apparent gunshot wounds to his head, neck and legs and hand, in the back of a boat parked in a Watertown, Massachusetts, backyard.

His friends weren't far behind in following him into federal custody.

After 10 hours of questioning that Friday, Kadyrbayev and Tazhayakov were detained the next day on alleged visa violations, according to Stahl.

Six days later, the backpack they'd thrown away was found -- this time in a New Bedford landfil. Inside was an assortment of fireworks, a jar of Vaseline and a homework assignment sheet from the University of Massachusetts-Dartmouth, among other items.

And on Wednesday, Kadyrbayev, Tazhayakov and Phillipos were in court accused of covering up for their friend, and hampering an investigation into the bloody attacks that jarred a city and a nation.